Trailer backup assist curvature control

ABSTRACT

A vehicle has a trailer backup steering input apparatus, a trailer backup assist control module coupled to the a trailer backup steering input apparatus, and an electric power assist steering system coupled to the trailer backup assist control module and. The trailer backup steering input apparatus is configured for outputting a trailer path curvature signal approximating a desired curvature for a path of travel of a trailer towably coupled to the vehicle. The trailer backup assist control module is configured for determining vehicle steering information as a function of the trailer path curvature signal. The electric power assist steering system is configured for controlling steering of steered wheels of the vehicle as a function of the vehicle steering information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 16/419,193, which was filed May 22, 2019, entitled “TrailerBackup Assist Curvature Control,” which is a continuation of U.S. patentapplication Ser. No. 14/482,604, which was filed Sep. 10, 2014, entitled“Trailer Backup Assist Curvature Control,” now U.S. Pat. No. 10,370,030,which is a continuation of U.S. patent application Ser. No. 13/336,060,which was filed on Dec. 23, 2011, entitled “Trailer Path CurvatureControl for Trailer Backup Assist,” now U.S. Pat. No. 8,909,426 whichclaims benefit from U.S. Provisional Patent Application No. 61/477,132,which was filed Apr. 19, 2011, entitled “Trailer Backup Assist CurvatureControl,” and which has a common applicant herewith and is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The disclosures made herein relate generally to steering assisttechnologies in vehicles and, more particularly, to trailer pathcurvature control for trailer backup assist.

BACKGROUND OF THE INVENTION

It is well-known that backing up a vehicle with a trailer attached is adifficult task for many drivers. This is particularly true for driversthat are untrained at backing with trailers such as, for example, thosethat drive with an attached trailer on an infrequent basis (e.g., haverented a trailer, use a personal trailer on an infrequent basis, etc.).One reason for such difficulty is that backing a vehicle with anattached trailer requires counter-steering that is opposite to normalsteering when backing the vehicle without a trailer attached and/orrequires braking to stabilize the vehicle-trailer combination before ajackknife condition occurs. Another reason for such difficulty is thatsmall errors in steering while backing a vehicle with an attachedtrailer are amplified thereby causing the trailer to depart from adesired path.

To assist the driver in steering a vehicle with trailer attached, atrailer backup assist system needs to know the driver's intention. Onecommon assumption with known trailer backup assist systems is that adriver of a vehicle with an attached trailer wants to back up straightand the system either implicitly or explicitly assumes a zero curvaturepath for the vehicle-trailer combination. Unfortunately most ofreal-world use cases of backing a trailer involve a curved path and,thus, assuming a path of zero curvature would significantly limitusefulness of the system. Some known systems assume that a path is knownfrom a map or path planner. To this end, some known trailer backupassist systems operate under a requirement that a trailer back-up pathis known before backing of the trailer commences such as, for example,from a map or a path planning algorithm. Undesirably, suchimplementations of the trailer backup assist systems are known to have arelatively complex Human Machine Interface (HMI) to specify the path,obstacles and/or goal of the backup maneuver. Furthermore, such systemsalso require some way to determine how well the desired path is beingfollowed and to know when the desired goal, or stopping point andorientation, has been met, using approaches such as cameras, inertialnavigation, or high precision GPS. These requirements lead to arelatively complex and costly system.

Therefore, implementing trailer backup assist using a trailer pathcurvature control approach that is relatively simple and that enables anintuitive vehicle operator interface would be advantageous, desirableand useful.

SUMMARY OF THE INVENTION

Embodiments of the inventive subject matter are directed to trailerbackup assist functionality that provides for controlling curvature of apath of a trailer attached to a vehicle. More specifically, trailerbackup assist functionality configured in accordance with embodiments ofthe disclosed subject matter provide for such trailer path curvaturecontrol by allowing a driver of the vehicle to specify a desired path ofthe trailer by inputting a desired trailer path curvature as the backupmaneuver of the vehicle and trailer progresses. In response to such pathof the trailer being specified by the driver, embodiments of theinventive subject matter control a power assisted steering system (e.g.,electric power assisted steering (EPAS) system) of the vehicle forimplementing steering angle changes of steered wheels of the vehicle toachieve the specified trailer path. Kinematics of the vehicle and thetrailer are used to determine the steering angle changes that arerequired for achieving the specified trailer path. Accordingly,embodiments of the inventive subject matter provide for implementationof trailer backup assist functionality in a manner that is relativelysimple and that enables use of an intuitive vehicle operator interfacefor specifying trailer path curvature control.

In one embodiment of the inventive subject matter, a method ofcontrolling a path of travel of a trailer towably coupled to a vehicleduring backing of the trailer by the vehicle comprises a plurality ofoperations. An operation is performed for receiving trailer pathcurvature information characterizing a desired curvature for the path oftravel of the trailer and an operation is performed for determiningvehicle steering information through assessment of kinematicalinformation of a system defined by the vehicle and the trailer.Assessment of the kinematical information is performed as a function ofthe trailer path curvature information. Thereafter, an operation isperformed for generating a steering command for a steering system of thevehicle as a function of the vehicle steering information.

In another embodiment of the inventive subject matter, an electroniccontrol system having a set of instructions tangibly embodied on anon-transitory processor-readable medium thereof. The set ofinstructions are accessible from the non-transitory processor-readablemedium by at least one data processing device of the electroniccontroller system for being interpreted thereby. The set of instructionsis configured for causing the at least one data processing device tocarry out an operation for of operations receiving trailer pathcurvature information for a trailer towably connected to a vehicle, anoperations for determining vehicle steering information, and anoperations for generating a steering command for a steering system ofthe vehicle. The trailer path curvature information characterizes adesired curvature for the path of travel of the trailer during backingof the trailer by the vehicle. The vehicle steering information isdetermined through assessment of kinematical information of a systemdefined by the vehicle and the trailer. Such assessment of thekinematical information is performed as a function of the trailer pathcurvature information. The steering command is generated as a functionof the vehicle steering information.

In another embodiment of the inventive subject matter, a vehiclecomprises a trailer backup steering input apparatus, a trailer backupassist control module coupled to the a trailer backup steering inputapparatus, and an electric power assist steering system coupled to thetrailer backup assist control module and. The trailer backup steeringinput apparatus is configured for outputting a trailer path curvaturesignal approximating a desired curvature for a path of travel of atrailer towably coupled to the vehicle. The trailer backup assistcontrol module is configured for determining vehicle steeringinformation as a function of the trailer path curvature signal. Theelectric power assist steering system is configured for controllingsteering of steered wheels of the vehicle as a function of the vehiclesteering information.

In another embodiment of the inventive subject matter, a trailer backupassist system for a vehicle backing a trailer includes a steering inputapparatus that provides a desired curvature for the trailer. The trailerbackup assist system also includes a control module that generates asteering command for the vehicle to guide the trailer on the desiredcurvature based on a hitch angle and a kinematic relationship determinedbetween the vehicle and the trailer.

In another embodiment of the inventive subject matter, a trailer backupassist system for a vehicle backing a trailer includes a camera-basedapparatus that determines a hitch angle between a vehicle and a trailer.The trailer backup assist system also includes a steering inputapparatus that commands a path of the trailer. Further, the trailerbackup assist system includes a control module that generates a steeringcommand for guiding the trailer on the path based on the hitch angle anda kinematic relationship between the vehicle and the trailer. Apower-steering system controls steered wheels of the vehicle based onthe steering command.

In yet another embodiment of the inventive subject matter, a method ofreversing a trailer includes a step of determining a kinematicrelationship between a vehicle and the trailer. The method also includesa step of determining a hitch angle between the vehicle and the trailer.Also, the method includes a step of commanding a path of the trailer. Inaddition, the method includes a step of generating a steering commandfor guiding the trailer on the path based on the hitch angle and thekinematic relationship. The method further includes a step ofcontrolling steered wheels of the vehicle with a power-steering systembased on the steering command.

These and other objects, embodiments, advantages and/or distinctions ofthe disclosed subject matter will become readily apparent upon furtherreview of the following specification, associated drawings and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a vehicle configured for performing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter embodiment;

FIG. 2 shows a preferred embodiment of the trailer backup steering inputapparatus discussed in reference to FIG. 1;

FIG. 3 shows an example of a trailer backup sequence implemented usingthe trailer backup steering input apparatus discussed in reference toFIG. 2;

FIG. 4 shows a method for implementing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter;

FIG. 5 is a diagrammatic view showing a kinematic model configured forproviding information utilized in providing trailer backup assistfunctionality in accordance with the inventive subject matter;

FIG. 6 is a graph showing an example of a trailer path curvaturefunction plot for a rotary-type trailer backup steering input apparatusconfigured in accordance with the inventive subject matter; and

FIG. 7 is a diagrammatic view showing a relationship between hitch angleand steered angle as it relates to determining a jackknife angle for avehicle/trailer system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inventive subject matter is directed to providing trailer backupassist functionality in a manner that is relatively low cost and thatoffers an intuitive user interface. In particular, such trailer backupassist functionality provides for controlling curvature of a path oftravel of a trailer attached to a vehicle (i.e., trailer path curvaturecontrol) by allowing a driver of the vehicle to specify a desired pathof the trailer by inputting a desired trailer path curvature as thebackup maneuver of the vehicle and trailer progresses. Although acontrol knob, a set of virtual buttons, or a touch screen can each beimplemented for enabling trailer path curvature control, the inventivesubject matter is not unnecessarily limited to any particularconfiguration of interface through which a desired trailer pathcurvature is inputted. Furthermore, in the case where a steering wheelcan be mechanically decoupled from steered wheels of the vehicle, thesteering wheel can also be used as an interface through which a desiredtrailer path curvature is inputted. As will be discussed herein ingreater detail, kinematical information of a system defined by thevehicle and the trailer are used to calculate a relationship (i.e.,kinematics) between the trailer's curvature and the steering angle ofthe vehicle for determining steering angle changes of the vehicle forachieving the specified trailer path. Steering commands corresponding tothe steering angle changes are used for controlling a steering system ofthe vehicle (e.g., electric power assisted steering (EPAS) system) ofthe vehicle for implementing steering angle changes of steered wheels ofthe vehicle to achieve (e.g., to approximate) the specified path oftravel of the trailer.

Referring to FIG. 1, an embodiment of a vehicle 100 configured forperforming trailer backup assist functionality in accordance with theinventive subject matter is shown. A trailer backup assist system 105 ofthe vehicle 100 controls the curvature of path of travel of the trailer110 that is attached to the vehicle 100. Such control is accomplishedthrough interaction of a power assisted steering system 115 of thevehicle 100 and the trailer backup assist system 105. During operationof the trailer backup assist system 105 while the vehicle 100 is beingreversed, a driver of the vehicle 100 is sometimes limited in the mannerin which he/she can make steering inputs via a steering wheel of thevehicle 100. This is because in certain vehicles the trailer backupassist system 105 is in control of the power assisted steering system115 and the power assisted steering system 115 is directly coupled tothe steering wheel (i.e., the steering wheel of the vehicle 100 moves inconcert with steered wheels of the vehicle 100). As is discussed belowin greater detail, a human machine interface (HMI) of the backup assistsystem 105 is used for commanding changes in curvature of a path of thetrailer 110 such as a knob, thereby decoupling such commands from beingmade at the steering wheel of the vehicle 100. However, some vehiclesconfigured to provide trailer backup assist functionality in accordancewith the inventive subject matter will have the capability toselectively decouple steering movement from movement of steerable wheelsof the vehicle, thereby allowing the steering wheel to be used forcommanding changes in curvature of a path of a trailer during suchtrailer backup assist.

The trailer backup assist system 105 includes a trailer backup assistcontrol module 120, a trailer backup steering input apparatus 125, and ahitch angle detecting apparatus 130. The trailer backup assist controlmodule 120 is connected to the trailer backup steering input apparatus125 and the hitch angle detecting apparatus 130 for allowingcommunication of information therebetween. It is disclosed herein thatthe trailer backup steering input apparatus can be coupled to thetrailer backup assist control module 120 in a wired or wireless manner.The trailer backup assist system control module 120 is attached to apower-steering assist control module 135 of the power-steering assistsystem 115 for allowing information to be communicated therebetween. Asteering angle detecting apparatus 140 of the power-steering assistsystem 115 is connected to the power-steering assist control module 125for providing information thereto. The trailer backup assist system isalso attached to a brake system control module 145 and a powertraincontrol module 150 for allowing communication of informationtherebetween. Jointly, the trailer backup assist system 105, thepower-steering assist system 115, the brake system control module 145,the powertrain control module 150 define a trailer backup assistarchitecture configured in accordance with an embodiment of theinventive subject matter.

The trailer backup assist control module 120 is configured forimplementing logic (i.e., instructions) for receiving information fromthe trailer backup steering input apparatus 125, the hitch angledetecting apparatus 130, the power-steering assist control module 135,the brake system control module 145, and the powertrain control module150. The trailer backup assist control module 120 (e.g., a trailercurvature algorithm thereof) generates vehicle steering information as afunction of all or a portion of the information received from thetrailer backup steering input apparatus 125, the hitch angle detectingapparatus 130, the power-steering assist control module 135, the brakesystem control module 145, and the powertrain control module 150.Thereafter, the vehicle steering information is provided to thepower-steering assist control module 135 for affecting steering of thevehicle 100 by the power-steering assist system 115 to achieve acommanded path of travel for the trailer 110.

The trailer backup steering input apparatus 125 provides the trailerbackup assist control module 120 with information defining the commandedpath of travel of the trailer 110 to the trailer backup assist controlmodule 120 (i.e., trailer steering information). The trailer steeringinformation can include information relating to a commanded change inthe path of travel (e.g., a change in radius of path curvature) andinformation relating to an indication that the trailer is to travelalong a path defined by a longitudinal centerline axis of the trailer(i.e., along a substantially straight path of travel). As will bediscussed below in detail, the trailer backup steering input apparatus125 preferably includes a rotational control input device for allowing adriver of the vehicle 100 to interface with the trailer backup steeringinput apparatus 125 to command desired trailer steering actions (e.g.,commanding a desired change in radius of the path of travel of thetrailer and/or commanding that the trailer travel along a substantiallystraight path of travel as defined by a longitudinal centerline axis ofthe trailer). In a preferred embodiment, the rotational control inputdevice is a knob rotatable about a rotational axis extending through atop surface/face of the knob. In other embodiments, the rotationalcontrol input device is a knob rotatable about a rotational axisextending substantially parallel to a top surface/face of the knob.

Some vehicles (e.g., those with active front steer) have apower-steering assist system configuration that allows a steering wheelto be decoupled from movement of the steered wheels of such a vehicle.Accordingly, the steering wheel can be rotated independent of the mannerin which the power-steering assist system of the vehicle controls thesteered wheels (e.g., as commanded by vehicle steering informationprovided by to a power-steering assist system control module from atrailer backup assist system control module configured in accordancewith an embodiment of the inventive subject matter). As such, in thesetypes of vehicles where the steering wheel can be selectively decoupledfrom the steered wheels to allow independent operation thereof, trailersteering information of a trailer backup assist system configured inaccordance with the inventive subject matter can be provided throughrotation of the steering wheel. Accordingly, it is disclosed herein thatin certain embodiments of the inventive subject matter, the steeringwheel is an embodiment of a rotational control input device in thecontext of the inventive subject matter. In such embodiments, thesteering wheel would be biased (e.g., by an apparatus that isselectively engagable/activatable) to an at-rest position betweenopposing rotational ranges of motion.

The hitch angle detecting apparatus 130, which operates in conjunctionwith a hitch angle detection component 155 of the trailer 110, providesthe trailer backup assist control module 120 with information relatingto an angle between the vehicle 100 and the trailer 110 (i.e., hitchangle information). In a preferred embodiment, the hitch angle detectingapparatus 130 is a camera-based apparatus such as, for example, anexisting rear view camera of the vehicle 100 that images (i.e., visuallymonitors) a target (i.e., the hitch angle detection component 155)attached the trailer 110 as the trailer 110 is being backed by thevehicle 100. Preferably, but not necessarily, the hitch angle detectioncomponent 155 is a dedicated component (e.g., an item attachedto/integral with a surface of the trailer 110 for the express purpose ofbeing recognized by the hitch angle detecting apparatus 130.Alternatively, the hitch angle detecting apparatus 130 can be a devicethat is physically mounted on a hitch component of the vehicle 100and/or a mating hitch component of the trailer 110 for determining anangle between centerline longitudinal axes of the vehicle 100 and thetrailer 110.

The power-steering assist control module 135 provides the trailer backupassist control module 120 with information relating to a rotationalposition (e.g., angle) of the steering wheel angle and/or a rotationalposition (e.g., turning angle(s)) of steered wheels of the vehicle 100.In certain embodiments of the inventive subject matter, the trailerbackup assist control module 120 can be an integrated component of thepower steering assist system 115. For example, the power-steering assistcontrol module 135 can include a trailer back-up assist algorithm forgenerating vehicle steering information as a function of all or aportion of information received from the trailer backup steering inputapparatus 125, the hitch angle detecting apparatus 130, thepower-steering assist control module 135, the brake system controlmodule 145, and the powertrain control module 150.

The brake system control module 145 provides the trailer backup assistcontrol module 120 with information relating to vehicle speed. Suchvehicle speed information can be determined from individual wheel speedsas monitored by the brake system control module 145. In some instances,individual wheel speeds can also be used to determine a vehicle yaw rateand such yaw rate can be provided to the trailer backup assist controlmodule 120 for use in determining the vehicle steering information. Incertain embodiments, the trailer backup assist control module 120 canprovide vehicle braking information to the brake system control module145 for allowing the trailer backup assist control module 120 to controlbraking of the vehicle 100 during backing of the trailer 110. Forexample, using the trailer backup assist control module 120 to regulatespeed of the vehicle 100 during backing of the trailer 110 can reducethe potential for unacceptable trailer backup conditions. Examples ofunacceptable trailer backup conditions include, but are not limited to,a vehicle overspeed condition, a trailer jackknife condition as definedby an angular displacement limit relative to the vehicle 100 and thetrailer 110, and the like. It is disclosed herein that the backup assistcontrol module 120 can issue a signal corresponding to a notification(e.g., a warning) of an actual, impending, and/or anticipatedunacceptable trailer backup condition.

The powertrain control module 150 interacts with the trailer backupassist control module 120 for regulating speed and acceleration of thevehicle 100 during backing of the trailer 110. As mentioned above,regulation of the speed of the vehicle 100 is necessary to limit thepotential for unacceptable trailer backup conditions such as, forexample, jackknifing. Similar to high-speed considerations as theyrelate to unacceptable trailer backup conditions, high acceleration canalso lead to such unacceptable trailer backup conditions.

Referring now to FIG. 2, a preferred embodiment of the trailer backupsteering input apparatus 125 discussed in reference to FIG. 1 is shown.A rotatable control element in the form of a knob 170 is coupled to amovement sensing device 175. The knob 170 is biased (e.g., by a springreturn) to an at-rest position P(AR) between opposing rotational rangesof motion R(R), R(L). A first one of the opposing rotational ranges ofmotion R(R) is substantially equal to a second one of the opposingrotational ranges of motion R(L), R(R). To provide a tactile indicationof an amount of rotation of the knob 170, a force that biases the knob170 toward the at-rest position P(AR) can increase (e.g., non-linearly)as a function of the amount of rotation of the knob 170 with respect tothe at-rest position P(AR). Additionally, the knob 170 can be configuredwith position indicating detents such that the driver can positivelyfeel the at-rest position P(AR) and feel the ends of the opposingrotational ranges of motion R(L), R(R) approaching (e.g., soft endstops).

The movement sensing device 175 is configured for sensing movement ofthe knob 170 and outputting a corresponding signal (i.e., movementsensing device signal) to the trailer assist backup input apparatus 125shown in FIG. 1. The movement sensing device signal is generated as afunction of an amount of rotation of the knob 170 with respect to theat-rest position P(AR), a rate movement of the knob 170, and/or adirection of movement of the knob 170 with respect to the at-restposition P(AR). As will be discussed below in greater detail, theat-rest position P(AR) of the knob 170 corresponds to a movement sensingdevice signal indicating that the vehicle 100 should be steered suchthat the trailer 100 is backed along a substantially straight path asdefined by a centerline longitudinal axis of the trailer 110 when theknob 170 was returned to the at-rest position P(AR) and a maximumclockwise and anti-clockwise position of the knob 170 (i.e., limits ofthe opposing rotational ranges of motion R(R), R(L)) each correspond toa respective movement sensing device signal indicating a tightest radiusof curvature (i.e., most acute trajectory) of a path of travel of thetrailer 110 that is possible without the corresponding vehicle steeringinformation causing a jackknife condition. In this regard, the at-restposition P(AR) is a zero curvature commanding position with respect tothe opposing rotational ranges of motion R(R), R(L). It is disclosedherein that a ratio of a commanded curvature of a path of a trailer(e.g., radius of a trailer trajectory) and a corresponding amount ofrotation of the knob can vary (e.g., non-linearly) over each one of theopposing rotational ranges of motion P(L), P(R) of the knob 170. It isalso disclosed therein that the ratio can be a function of vehiclespeed, trailer geometry, vehicle geometry, hitch geometry and/or trailerload.

Use of the knob 170 decouples trailer steering inputs from being made ata steering wheel of the vehicle 100. In use, as a driver of the vehicle100 backs the trailer 110, the driver can turn the knob 170 to dictate acurvature of a path of the trailer 110 to follow and returns the knob170 to the at-rest position P(AR) for causing the trailer 110 to bebacked along a straight line. Accordingly, in embodiments of trailerbackup assist systems where the steering wheel remains physicallycoupled to the steerable wheels of a vehicle during backup of anattached trailer, a rotatable control element configured in accordancewith the inventive subject matter (e.g., the knob 170) provides a simpleand user-friendly means of allowing a driver of a vehicle to inputtrailer steering commands.

It is disclosed herein that a rotational control input device configuredin accordance with embodiments of the inventive subject matter (e.g.,the knob 170 and associated movement sensing device) can omit a meansfor being biased to an at-rest position between opposing rotationalranges of motion. Lack of such biasing allows a current rotationalposition of the rotational control input device to be maintained untilthe rotational control input device is manually moved to a differentposition. Preferably, but not necessarily, when such biasing is omitted,a means is provided for indicating that the rotational control inputdevice is positioned in a zero curvature commanding position (e.g., atthe same position as the at-rest position in embodiments where therotational control input device is biased). Examples of means forindicating that the rotational control input device is positioned in thezero curvature commanding position include, but are not limited to, adetent that the rotational control input device engages when in the zerocurvature commanding position, a visual marking indicating that therotational control input device is in the zero curvature commandingposition, an active vibratory signal indicating that the rotationalcontrol input device is in or approaching the zero curvature commandingposition, an audible message indicating that the rotational controlinput device is in of approaching the zero curvature commandingposition, and the like.

It is also disclosed herein that embodiments of the inventive subjectmatter can be configured with a control input device that is notrotational (i.e., a non-rotational control input device). Similar to arotational control input device configured in accordance withembodiments of the inventive subject matter (e.g., the knob 170 andassociated movement sensing device), such a non-rotational control inputdevice is configured to selectively provide a signal causing a trailerto follow a path of travel segment that is substantially straight and toselectively provide a signal causing the trailer to follow a path oftravel segment that is substantially curved. Examples of such anon-rotational control input device include, but are not limited to, aplurality of depressible buttons (e.g., curve left, curve right, andtravel straight), a touch screen on which a driver traces or otherwiseinputs a curvature for path of travel commands, a button that istranslatable along an axis for allowing a driver to input path of travelcommands, and the like.

The trailer backup steering input apparatus 125 can be configured toprovide various feedback information to a driver of the vehicle 100.Examples of situation that such feedback information can indicateinclude, but are not limited to, a status of the trailer backup assistsystem 105 (e.g., active, in standby (e.g., when driving forward toreduce the trailer angle), faulted, inactive, etc), that a curvaturelimit has been reached (i.e., maximum commanded curvature of a path oftravel of the trailer 110), etc. To this end, the trailer backupsteering input apparatus 125 can be configured to provide a tactilefeedback signal (e.g., a vibration through the knob 170) as a warning ifany one of a variety of conditions occur. Examples of such conditionsinclude, but are not limited to, the trailer 110 having jackknifed, thetrailer backup assist system 105 has had a failure, the trailer backupassist system 105 or other system of the vehicle 100 has predicted acollision on the present path of travel of the trailer 110, the trailerbackup system 105 has restricted a commanded curvature of a trailer'spath of travel (e.g., due to excessive speed or acceleration of thevehicle 100), and the like. Still further, it is disclosed that thetrailer backup steering input apparatus 125 can use illumination (e.g.,an LED 180) and/or an audible signal output (e.g., an audible outputdevice 185) to provide certain feedback information (e.g.,notification/warning of an unacceptable trailer backup condition).

Referring now to FIGS. 2 and 3, an example of using the trailer backupsteering input apparatus 125 for dictating a curvature of a path oftravel (POT) of a trailer (i.e., the trailer 110 shown in FIG. 1) whilebacking up the trailer with a vehicle (i.e., the vehicle 100 in FIGS. 1and 2) is shown. In preparation of backing the trailer 110, the driverof the vehicle 100 drives the vehicle 100 forward along a pull-thru path(PTP) to position the vehicle 100 and trailer 110 at a first backupposition B1. In the first backup position B1, the vehicle 100 andtrailer 110 are longitudinally aligned with each other such that alongitudinal centerline axis L1 of the vehicle 100 is aligned with(e.g., parallel with or coincidental with) a longitudinal centerlineaxis L2 of the trailer 110. It is disclosed herein that such alignmentof the longitudinal axes L1, L2 at the onset of an instance of trailerbackup functionality is not a requirement for operability of a trailerbackup assist system configured in accordance with the inventive subjectmatter.

After activating the trailer backup assist system 105 (e.g., before,after, or during the pull-thru sequence), the driver begins to back thetrailer 110 by reversing the vehicle 100 from the first backup positionB1. So long as the knob 170 of the trailer backup steering inputapparatus 125 remains in the at-rest position P(AR), the trailer backupassist system 105 will steer the vehicle 100 as necessary for causingthe trailer 110 to be backed along a substantially straight path oftravel as defined by the longitudinal centerline axis L2 of the trailer110 at the time when backing of the trailer 110 began. When the trailerreaches the second backup position B2, the driver rotates the knob 170to command the trailer 110 to be steered to the right (i.e., a knobposition R(R)). Accordingly, the trailer backup assist system 105 willsteer the vehicle 100 for causing the trailer 110 to be steered to theright as a function of an amount of rotation of the knob 170 withrespect to the at-rest position P(AR), a rate movement of the knob 170,and/or a direction of movement of the knob 170 with respect to theat-rest position P(AR). Similarly, the trailer 110 can be commanded tosteer to the left by rotating the knob 170 to the left. When the trailerreaches backup position B3, the driver allows the knob 170 to return tothe at-rest position P(AR) thereby causing the trailer backup assistsystem 105 to steer the vehicle 100 as necessary for causing the trailer110 to be backed along a substantially straight path of travel asdefined by the longitudinal centerline axis L2 of the trailer 110 at thetime when the knob 170 was returned to the at-rest position P(AR).Thereafter, the trailer backup assist system 105 steers the vehicle 100as necessary for causing the trailer 110 to be backed along thissubstantially straight path to the fourth backup position B4. In thisregard, arcuate portions of a path of travel POT of the trailer 110 aredictated by rotation of the knob 170 and straight portions of the pathof travel POT are dictated by an orientation of the centerlinelongitudinal axis L2 of the trailer when the knob 170 is in/returned tothe at-rest position P(AR).

FIG. 4 shows a method 200 for implementing trailer backup assistfunctionality in accordance with an embodiment of the inventive subjectmatter. In a preferred embodiment, the method 200 for implementingtrailer backup assist functionality can be carried out using the trailerbackup assist architecture discussed above in reference to the vehicle100 and trailer 110 of FIG. 1. Accordingly, trailer steering informationis provided through use of a rotational control input device (e.g., theknob 170 discussed in reference to FIG. 2).

An operation 202 is performed for receiving a trailer backup assistrequest. Examples of receiving the trailer backup assist request includeactivating the trailer backup assist system and providing confirmationthat the vehicle and trailer are ready to be backed. After receiving atrailer backup assist request (i.e., while the vehicle is beingreversed), an operation 204 is performed for receiving a trailer backupinformation signal. Examples of information carried by the trailerbackup information signal include, but are not limited to, informationfrom the trailer backup steering input apparatus 125, information fromthe hitch angle detecting apparatus 130, information from thepower-steering assist control module 135, information from the brakesystem control module 145, and information from the powertrain controlmodule 150. It is disclosed herein that information from the trailerbackup steering input apparatus 125 preferably includes trailer pathcurvature information characterizing a desired curvature for the path oftravel of the trailer, such as provided by the trailer backup steeringinput apparatus 125 discussed above in reference to FIGS. 1 and 2. Inthis manner, the operation 204 for receiving the trailer backupinformation signal can include receiving trailer path curvatureinformation characterizing the desired curvature for the path of travelof the trailer.

If the trailer backup information signal indicates that a change incurvature of the trailer's path of travel is requested (i.e., commandedvia the knob 170), an operation 206 is performed for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel. Otherwise, an operation 208 is performedfor determining vehicle steering information for maintaining a currentstraight-line heading of the trailer (i.e., as defined by thelongitudinal centerline axis of the trailer). Thereafter, an operation210 is performed for providing the vehicle steering information to apower-steering assist system of the vehicle, followed by an operation212 being performed for determining the trailer backup assist status. Ifit is determined that trailer backup is complete, an operation 214 isperformed for ending the current trailer backup assist instance.Otherwise the method 200 returns to the operation 204 for receivingtrailer backup information. Preferably, the operation for receiving thetrailer backup information signal, determining the vehicle steeringinformation, providing the vehicle steering information, and determiningthe trailer backup assist status are performed in a monitoring fashion(e.g., at a high rate of speed of a digital data processing device).Accordingly, unless it is determined that reversing of the vehicle forbacking the trailer is completed (e.g., due to the vehicle having beensuccessfully backed to a desired location during a trailer backup assistinstance, the vehicle having to be pulled forward to begin anothertrailer backup assist instance, etc), the method 200 will continually beperforming the operations for receiving the trailer backup informationsignal, determining the vehicle steering information, providing thevehicle steering information, and determining the trailer backup assiststatus.

It is disclosed herein that the operation 206 for determining vehiclesteering information for providing the requested change in curvature ofthe trailer's path of travel preferably includes determining vehiclesteering information as a function of trailer path curvature informationcontained within the trailer backup information signal. As will bediscussed below in greater detail, determining vehicle steeringinformation can be accomplished through a low order kinematic modeldefined by the vehicle and the trailer. Through such a model, arelationship between the trailer path curvature and commanded steeringangles of steered wheels of the vehicle can be generated for determiningsteering angle changes of the steered wheels for achieving a specifiedtrailer path curvature. In this manner, the operation 206 fordetermining vehicle steering information can be configured forgenerating information necessary for providing trailer path curvaturecontrol in accordance with the inventive subject matter.

In some embodiments of the inventive subject matter, the operation 210for providing the vehicle steering information to the power-steeringassist system of the vehicle causes the steering system to generate acorresponding steering command as a function of the vehicle steeringinformation. The steering command is interpretable by the steeringsystem and is configured for causing the steering system to move steeredwheels of the steering system for achieving a steered angle as specifiedby the vehicle steering information. Alternatively, the steering commandcan be generated by a controller, module or computer external to thesteering system (e.g., a trailer backup assist control module) and beprovided to the steering system.

In parallel with performing the operations for receiving the trailerbackup information signal, determining the vehicle steering information,providing the vehicle steering information, and determining the trailerbackup assist status, the method 200 performs an operation 216 formonitoring the trailer backup information for determining if anunacceptable trailer backup condition exists. Examples of suchmonitoring include, but are not limited to assessing a hitch angle todetermine if a hitch angle threshold is exceeded, assessing a backupspeed to determine if a backup speed threshold is exceeded, assessingvehicle steering angle to determining if a vehicle steering anglethreshold is exceeded, and the like. If it is determined that anunacceptable trailer backup condition exists, an operation 218 isperformed for causing the current path of travel of the trailer to beinhibited (e.g., stopping motion of the vehicle), followed by theoperation 214 being performed for ending the current trailer backupassist instance. It is disclosed herein that prior to and/or inconjunction with causing the current trailer path to be inhibited, oneor more actions (e.g., operations) can be implemented for providing thedriver with feedback (e.g., a warning) that such an unacceptable trailerangle condition is impending or approaching. In one example, if suchfeedback results in the unacceptable trailer angle condition beingremedied prior to achieving a critical condition, the method cancontinue with providing trailer backup assist functionality inaccordance with operations 204-212. Otherwise, the method can proceed tooperation 214 for ending the current trailer backup assist instance. Inconjunction with performing the operation 214 for ending the currenttrailer backup assist instance, an operation can be performed forcontrolling movement of the vehicle to correct or limit a jackknifecondition (e.g., steering and/or decelerating the vehicle to precludethe hitch angle from being exceeded).

Turning now to a discussion of a kinematic model used to calculate arelationship between a curvature of a path of travel of a trailer andthe steering angle of a vehicle towing the trailer, a low orderkinematic model can be desirable for a trailer back-up assist systemconfigured in accordance with some embodiments of the inventive subjectmatter. To achieve such a low order kinematic model, certain assumptionsare made with regard to parameters associated with the vehicle/trailersystem. Examples of such assumptions include, but are not limited to,the trailer being backed by the vehicle at a relatively low speed,wheels of the vehicle and the trailer having negligible (e.g., no) slip,tires of the vehicle and the trailer having negligible (e.g., no)deformation, actuator dynamics of the vehicle being negligible, thevehicle and the trailer exhibiting negligible (e.g., no) roll or pitchmotions.

As shown in FIG. 5, for a system defined by a vehicle 302 and a trailer304, the kinematic model 300 is based on various parameters associatedwith the vehicle 302 and the trailer 304. These kinematic modelparameters include:

-   -   δ: steering angle at steered front wheels 306 of the vehicle        302;    -   α: yaw angle of the vehicle 302;    -   β: yaw angle of the trailer 304;    -   γ: hitch angle (γ=β−α);    -   W: wheel base of the vehicle 302;    -   L: length between hitch point 308 and rear axle 310 of the        vehicle 302;    -   D: length between hitch point 308 and axle 312 of the trailer        304; and    -   r₂: curvature radius for the trailer 304.

The kinematic model 300 of FIG. 5 reveals a relationship between trailerpath radius of curvature r₂ at the midpoint 314 of an axle 306 of thetrailer 304, steering angle δ of the steered wheels 306 of the vehicle302, and the hitch angle γ. As shown in the equation below, thisrelationship can be expressed to provide the trailer path curvature κ2such that, if γ is given, the trailer path curvature κ2 can becontrolled based on regulating the steering angle δ (where β(·) istrailer yaw rate and η(·) is trailer velocity).

$\kappa_{2} = {\frac{1}{r_{2}} = {\frac{\overset{.}{\beta}}{\overset{.}{\eta}} = \frac{{( {W + \frac{KV^{2}}{g}} )\sin\;\gamma} + {L\;\cos\;\gamma\;\tan\;\beta}}{D( {{( {W + \frac{KV^{2}}{g}} )\cos\;\gamma} - {L\;\sin\;\gamma\;\tan\;\delta}} )}}}$

Or, this relationship can be expressed to provide the steering angle δas a function of trailer path curvature κ2 and hitch angle γ.

$\delta = {{\tan^{- 1}( \frac{( {W + \frac{KV^{2}}{g}} )\lbrack {{\kappa_{2}D\;\cos\;\gamma}\; - {\sin\;\gamma}} \rbrack}{{{DL}\;\kappa_{2}\sin\;\gamma} + {L\;\cos\;\gamma}} )} = {F( {\gamma,\kappa_{2},K} )}}$

Accordingly, for a particular vehicle and trailer combination, certainkinematic model parameters (e.g., D, W and L) are constant and assumedknown. V is the vehicle longitudinal speed and g is the acceleration dueto gravity. K is a speed dependent parameter which when set to zeromakes the calculation of steering angle independent of vehicle speed.For example, vehicle-specific kinematic model parameters can bepredefined in an electronic control system of a vehicle andtrailer-specific kinematic model parameters can be inputted by a driverof the vehicle. Trailer path curvature κ₂ is determined from the driverinput via a trailer backup steering input apparatus. Through the use ofthe equation for providing steering angle, a corresponding steeringcommand can be generated for controlling a steering system (e.g., anactuator thereof) of the vehicle.

FIG. 6 shown an example of a trailer path curvature function plot 400for a rotary-type trailer backup steering input apparatus (e.g., thetrailer backup steering input apparatus 125 discussed above in referenceto FIGS. 1 and 2). A value representing trailer path curvature (e.g.,trailer path curvature κ2) is provided as an output signal from therotary-type trailer backup steering input apparatus as a function ofuser input movement. In this example, a curve 402 specifying trailerpath curvature relative to user input (e.g., amount of rotation) at arotary input device (e.g., a knob) is defined by a cubic function.However, a skilled person will appreciate that embodiments of theinventive subject matter are not limited to any particular functionbetween a magnitude and/or rate of input at a trailer backup steeringinput apparatus (e.g., knob rotation) and a resulting trailer pathcurvature value.

Referring to FIG. 5, in preferred embodiments of the inventive subjectmatter, it is desirable to limit the potential for the vehicle 302 andthe trailer 304 to attain a jackknife angle (i.e., the vehicle/trailersystem achieving a jackknife condition). A jackknife angle γ(j) refersto a hitch angle γ that cannot be overcome by the maximum steering inputfor a vehicle such as, for example, the steered front wheels 306 of thevehicle 302 being moved to a maximum steered angle δ at a maximum rateof steering angle change. The jackknife angle γ(j) is a function of amaximum wheel angle for the steered wheel 306 of the vehicle 302, thewheel base W of the vehicle 302, the distance L between hitch point 308and the rear axle 310 of the vehicle 302, and the length D between thehitch point 308 and the axle 312 of the trailer 304. When the hitchangle γ for the vehicle 302 and the trailer 304 achieves or exceeds thejackknife angle γ(j), the vehicle 302 must be pulled forward to reducethe hitch angle γ. Thus, for limiting the potential for avehicle/trailer system attaining a jackknife angle, it is preferable tocontrol the yaw angle of the trailer while keeping the hitch angle ofthe vehicle/trailer system relatively small.

Referring to FIGS. 5 and 7, a steering angle limit for the steered frontwheels 306 requires that the hitch angle γ cannot exceed the jackknifeangle γ (j), which is also referred to as a critical hitch angle. Thus,under the limitation that the hitch angle γ cannot exceed the jackknifeangle γ(j), the jackknife angle γ (j) is the hitch angle γ thatmaintains a circular motion for the vehicle/trailer system when thesteered wheels 306 are at a maximum steering angle δ(max). The steeringangle for circular motion with hitch angle is defined by the followingequation.

${\tan\delta_{\max}} = \frac{w\;\sin\;\gamma_{\max}}{D + {L\;\cos\;\gamma_{\max}}}$

Solving the above equation for hitch angle allows jackknife angle γ(j)to be determined. This solution, which is shown in the followingequation, can be used in implementing trailer backup assistfunctionality in accordance with the inventive subject matter formonitoring hitch angle in relation to jackknife angle.

$\cos\;\overset{\_}{\gamma}\frac{{- b} \pm \sqrt{b^{2} - {4ac}}}{2a}$

where,

-   -   a=L² tan²δ(max)+W²;    -   b=2 LD tan²δ(max); and    -   c=D² tan²δ(max)−W².

Referring now to instructions processible by a data processing device,it will be understood from the disclosures made herein that methods,processes and/or operations adapted for carrying out trailer backupassist functionality as disclosed herein are tangibly embodied bynon-transitory computer readable medium having instructions thereon thatare configured for carrying out such functionality. The instructions aretangibly embodied for carrying out the method 200 disclosed anddiscussed above and can be further configured for limiting the potentialfor a jackknife condition such as, for example, by monitoring jackknifeangle through use of the equations discussed in reference to FIGS. 5 and7. The instructions may be accessible by one or more data processingdevices from a memory apparatus (e.g. RAM, ROM, virtual memory, harddrive memory, etc), from an apparatus readable by a drive unit of a dataprocessing system (e.g., a diskette, a compact disk, a tape cartridge,etc) or both. Accordingly, embodiments of computer readable medium inaccordance with the inventive subject matter include a compact disk, ahard drive, RAM or other type of storage apparatus that has imagedthereon a computer program (i.e., instructions) configured for carryingout trailer backup assist functionality in accordance with the inventivesubject matter.

In a preferred embodiment of the inventive subject matter, a trailerback-up assist control module (e.g., the trailer back-up assist controlmodule 120 discussed above in reference to FIG. 1) comprises such a dataprocessing device, such a non-transitory computer readable medium, andsuch instructions on the computer readable medium for carrying outtrailer backup assist functionality (e.g., in accordance with the method200 discussed above in reference to FIG. 2). To this end, the trailerback-up assist control module can comprise various signal interfaces forreceiving and outputting signals. A trailer back-up assist controlmodule in the context of the inventive subject matter can be any controlmodule of an electronic control system that provides for trailer back-upassist control functionality in accordance with the inventive subjectmatter. Furthermore, it is disclosed herein that such a controlfunctionality can be implemented within a standalone control module(physically and logically) or can be implemented logically within two ormore separate but interconnected control modules (e.g., of an electroniccontrol system of a vehicle) In one example, trailer back-up assistcontrol module in accordance with the inventive subject matter isimplemented within a standalone controller unit that provides onlytrailer backup assist functionality. In another example, trailer backupassist functionality in accordance with the inventive subject matter isimplemented within a standalone controller unit of an electronic controlsystem of a vehicle that provides trailer backup assist functionality aswell as one or more other types of system control functionality of avehicle (e.g., anti-lock brake system functionality, steering powerassist functionality, etc). In still another example, trailer backupassist functionality in accordance with the inventive subject matter isimplemented logically in a distributed manner whereby a plurality ofcontrol units, control modules, computers, or the like (e.g., anelectronic control system) jointly carry out operations for providingsuch trailer backup assist functionality.

In the preceding detailed description, reference has been made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration specific embodiments in which the inventive subjectmatter may be practiced. These embodiments, and certain variantsthereof, have been described in sufficient detail to enable thoseskilled in the art to practice embodiments of the inventive subjectmatter. It is to be understood that other suitable embodiments may beutilized and that logical, mechanical, chemical and electrical changesmay be made without departing from the spirit or scope of such inventivedisclosures. To avoid unnecessary detail, the description omits certaininformation known to those skilled in the art. The preceding detaileddescription is, therefore, not intended to be limited to the specificforms set forth herein, but on the contrary, it is intended to coversuch alternatives, modifications, and equivalents, as can be reasonablyincluded within the spirit and scope of the appended claims.

What is claimed is:
 1. A vehicle comprising: a hitch configured to tow atrailer; one or more steered wheels; a steering wheel configurable tosteer the one or more steered wheels; and a trailer backup assist systemfor backing the trailer, the trailer backup assist system comprising: ahitch angle detecting apparatus determining a hitch angle between thevehicle and the trailer; a steering input apparatus providing a path oftravel for the trailer during backing of the trailer; a control modulegenerating a steering command for the vehicle to guide the trailer onthe path based on the hitch angle and a kinematic relationshipdetermined between the vehicle and the trailer; and a power-steeringsystem for steering the vehicle based on the steering command.
 2. Thevehicle of claim 1, wherein the kinematic relationship is based on atleast length of the trailer, wheel base of the vehicle and steeringangle of the vehicle.
 3. The vehicle of claim 1, wherein the steeringcommand provides a desired curvature of the path of the trailer relativeto a longitudinal centerline axis of the trailer.
 4. The vehicle ofclaim 3, wherein the desired curvature is relative to a zero curvaturecommanding position that defines backward movement of the trailer alonga substantially straight path defined by the longitudinal centerlineaxis of the trailer.
 5. The vehicle of claim 4, wherein the steeringinput apparatus includes a knob rotatable in opposing directions from anintermediate position to end positions, defining a plurality of rotatedpositions therebetween that correspond with ascending desiredcurvatures.
 6. The vehicle of claim 5, wherein the control moduledefines the end positions of the knob with a maximum curvature for thetrailer to prevent the hitch angle from exceeding a critical hitchangle.
 7. The vehicle of claim 6, wherein the knob includes limits ofrotational movement at the end positions.
 8. The vehicle of claim 5,wherein the knob is spring biased in the intermediate position, whichcorresponds with a desired curvature of zero for backing the traileralong a substantially straight path of travel.
 9. The vehicle of claim2, wherein the steering input apparatus includes a control elementmovable between at least a first position having a first desiredcurvature for backing the trailer along a substantially straighttrajectory and a second position having a second desired curvature forbacking the trailer along an arcuate trajectory.
 10. The vehicle ofclaim 1, wherein the power-steering system controls forward steeredwheels of the vehicle based on the steering command generated from thecontrol module.
 11. A vehicle comprising: a hitch configured to tow atrailer; steered wheels; a steering wheel configurable to steer thesteered wheels; and a trailer backup assist system for backing thetrailer, the trailer backup system comprising: a camera-based apparatusdetermining a hitch angle between a vehicle and a trailer; a rotatablesteering input apparatus commanding a path of the trailer, wherein therotatable steering input apparatus is separate from the steering wheel;a control module generating a steering command for guiding the traileron the path based on the hitch angle and a kinematic relationshipbetween the vehicle and the trailer; and a power-steering systemcontrolling the steered wheels of the vehicle based on the steeringcommand, wherein the steering command provides a desired curvature ofthe path of the trailer relative to a longitudinal centerline axis ofthe trailer.
 12. The vehicle of claim 11, wherein the kinematicrelationship is based on at least a length of the trailer, a wheel baseof the vehicle and a steering angle of the vehicle.
 13. The vehicle ofclaim 11, wherein the rotatable steering input apparatus is coupled withan interior surface of the vehicle for a driver of the vehicle toprovide the path of the trailer.
 14. The vehicle of claim 11, whereinthe rotatable steering input apparatus includes a control elementmovable between a first position for backing the trailer along asubstantially straight trajectory and a second position for backing thetrailer along an arcuate trajectory.
 15. The vehicle of claim 11,wherein the path commanded by the rotatable steering input apparatusincludes the desired curvature relative to the longitudinal centerlineaxis of the trailer, wherein the desired curvature commands a curvaturepath of the trailer that allows continuous backup of the trailer that isbelow a theoretical jackknife point.
 16. The vehicle of claim 15,wherein the rotatable steering input apparatus includes a controlelement movable between at least a first position with the desiredcurvature of zero and a second position with the desired curvaturegreater than zero.
 17. The vehicle of claim 15, wherein the rotatablesteering input apparatus is a knob rotatable in opposing directions froman intermediate position to end positions, defining a plurality ofrotated positions therebetween that correspond with desired curvaturesincreasing as the knob is rotated away from the intermediate position.18. The vehicle of claim 17, wherein the knob is prevented from rotatingbeyond the end positions and is spring biased in the intermediateposition, which corresponds with a desired curvature of zero for backingthe trailer along a substantially straight trajectory.
 19. The vehicleof claim 18, wherein the control module defines the end positions of theknob with a maximum curvature for the trailer based on the kinematicrelationship to prevent the hitch angle from approaching a jackknifeangle.